This invention relates to an improved automobile construction and a method of manufacturing and assembling such an automobile that provides for greater structural strength per unit weight and simplified assembly relative to traditionally produced monocoque and spaceframe vehicles.
Conventional manufacturing methods for assembling either a monocoque or spaceframe vehicle as shown, for example, in FIGS. 17 and 18 are capital intensive processes that include, as a generalization, a body shop where the structural panels are assembled, a paint shop where the structure is coated and painted, and a general assembly line where all other components are added to the structure. In these known methods the general material flow for the vehicle structure is from raw materials to a body shop, usually via a stamping plant for a monocoque or an extruder for many of the structural parts in a spaceframe, where the parts are assembled into the complete vehicle structure. This vehicle shell or frame, called the body in white, is then sent to a paint shop where it is coated and painted as a complete structure. After painting, trim and other components are added to the structure during the final assembly process.
More specifically, the standard production process for automotive bodies manufactured in mass production is to stamp the panels, typically out of steel, assemble these panels into subassemblies, almost exclusively through spot or laser welding, and then assemble these subassemblies, again by welding, into a vehicle body. Multiple stamping tools are used to form each of the components that make up every subassembly, and an additional assortment of tools or robots are used to assemble the components. As a simplification, the major subassemblies of the underbody, side assemblies, and roof assembly can be used to depict the structure of a typical full vehicle body in white assembly process. The first step of the simplified whole vehicle assembly process is to place the underbody subassembly on a framing fixture. Then the two side subassemblies (passenger and driver side subassemblies) are loaded into the fixture, located, and secured. U.S. Pat. No. 5,480,208 discloses a method of accurately aligning the body side panels. This step is followed by adding the roof assembly to the top of the structure, generally in a separate fixture from the bodyside installation, to form the vehicle body structure. All other structural subassemblies are then added to the vehicle body structure forming the complete body in white. The closure panels (doors) are then secured to the body in white to form the entire vehicle body construction. This is the stage at which traditional vehicles are painted before all of the other components and trim are assembled to the structure.
The traditional method as described above is not the only known method for assembling a monocoque or unibody vehicle from stamped panels. As a deviation from the method of assembling the two side panels to the floor panel followed by the roof panel, for example, U.S. Pat. No. 4,759,489 discloses a method of building an automotive body in separate upper and lower body modules, referred to as the roof area and floor area respectively. Another fabrication approach is discussed in U.S. Pat. No. 6,493,920 where an open-top cab module is assembled to create a metal base frame. The exterior body panels are then attached to the base frame and the interior cab module trim components are installed. The roof is subsequently fitted onto this trimmed out lower vehicle section. These are examples of assembly techniques for unibody construction as shown in FIG. 17.
As a completely separate vehicle architecture from a unibody construction, a spaceframe design utilizes a rigid framework for the body structure in place of the multitude of formed panels. The spaceframe architecture is used in some limited production vehicles but is more typically used in highly specialized vehicles where the design and manufacturing is unique to the specific vehicle, as is the case with many racing vehicles. For example, U.S. Pat. No. 6,719,364 shows a roll cage type spaceframe attached to a floor pan and a “unitary structure of cage sufficient to accommodate both passenger and power plant” (Col 3, lines 42-43) where the exterior body panels are attached from the inside (Col 3, lines 51-52). Other patents related to spaceframe vehicle construction include the one-piece spaceframes as discussed in U.S. Pat. Nos. 4,735,355; 4,660,345; 4,045,075; and 6,824,204. Various methods of joining the components in a spaceframe are described in U.S. Pat. Nos. 5,338,080; 4,986,597; 5,767,476; 5,715,643; and 5,343,666.
In other words, the traditional method for assembling the body of a mass-produced vehicle is through stamped steel body panel construction while an alternative method to create the vehicle structure which is less mainstream, but successfully used in the industry, is spaceframe construction. Both of these body construction methods use a common, traditional assembly procedure for the trim, hardware, and other components as above described and shown in FIGS. 17 and 18. In short, the components outside of the vehicle cabin are attached to the structure and the components, such as the interior trim, that exist inside of the vehicle body are passed through the door openings of the vehicle's body and attached to the structure. The internal components can be loaded and installed with or without the door installed, in the former case the door must simply be opened to pass components into interior of the vehicle. In either case, the components enter the fully assembled vehicle structure through either the front or rear side door openings before being attached. The exception to this is in a limited number of vehicles where the roof is not installed as a part of the structure during the trim assembly process. This allows the option of installing components to the interior of the vehicle cabin by passing them through the open roof area in addition to the open door areas. Even in the known roof-off fabrication methods, the vehicle base is still completely assembled in the traditional manner with the only significant difference being that the interior components can be installed through the open roof access instead of relying on only the door and window openings. For example, none of these assembly approaches utilize a door assembly method whereby the door components can be assembled to the door, either before or after the doors are attached to the body, by loading them to the cavity between the doors interior and exterior panels from the outside of the vehicle prior to the installation of the exterior panel as shown in FIG. 13.
A vehicle with the traditional stamped body panel construction involves an exorbitant manufacturing cost from both tooling and assembly points of view. The creation of all the large stampings that make up the structure is tooling intensive and the body shop required to assemble the structure adds significant additional costs for a new vehicle model. In order to amortize these substantial costs, a manufacturing plant may need to build as many as one hundred thousand vehicles per year over a model life of four to six years. This vehicle architectural approach requires a high volume production or high pricing to offset the upfront capital, lacks manufacturing flexibility as a result of the highly formed parts that are not easy to change, and does not easily allow the ability to change designs after only one or two model years. Such a system is not well suited for profitably producing vehicles in smaller volumes. The alternative design methodology of a spaceframe reduces the upfront costs by eliminating many of the formed parts from the vehicle structure. Both of these vehicle architectures have been nearly exclusively applied to painted vehicles in which the assembled structure is coated and painted after the welding is completed. The substantial capital investment and plant floor space required for a paint line at the assembly plants further restrict the flexibility and inhibit creation of manufacturing facilities in light industrial zones.
In spite of the advancements made in spaceframe construction, lightweight vehicles and manufacturing techniques, there remains a pressing need to further enhance safety, improve fuel economy and reduce manufacturing and distribution costs. In contrast to the traditional manufacturing processes mentioned above, an object of the present invention is to provide a method of design, fabrication and repair which creates a vehicle architecture that can be produced without a high tooling investment for stamped body panels, without a capital intensive body shop to assemble the structure, and without the need for a cost prohibitive paint line. These production attributes provide flexibility, modularity, and ease of fabrication and repair with the intent to significantly reduce investment costs.
Another object is to achieve a vehicle architecture that reduces weight, improves impact performance, dramatically increases production flexibility, allows for shorter design time between models, and creates a streamlined delivery system to reduce vehicle inventories and eliminate excessive volumes. This invention is able to achieve these and other objectives by radically departing from the steel unitized body approach or singular spaceframe structure and instead utilize a modular, multi-material, spaceframe architecture.
One aspect of the present invention is a platform comprised of a core frame, a front sub-frame, a rear sub-frame, and a roof subassembly, all of which are all bolted together. (The term “bolted” as used in this disclosure refers to a semi-permanent fastening system which can be disconnected with reasonable effort and the use of only common hand tools.) The core sub-frame is basically the structural boundary of the occupant compartment that exists below the belt line. In an embodiment of the present invention the core sub-frame can also contain the front impact mitigation structure as a design that increases the crush zone. The front sub-frame holds the steering, front tires and suspension, and other front mounted components. An embodiment of the present invention also includes the front crush structure as a part of the front sub-frame subassembly for an increased case of repair and assembly. The rear sub-frame holds the rear impact mitigation structure, rear tires and suspension, and other rear mounted components. The roof subassembly creates and seals off the vehicle cabin above the belt line and contributes to the vehicles structural performance and integrity while carrying the roof panel, windshield, trim, and other components. The novel vehicle platform configuration allows this roof system to be added to the vehicle after the interior trim is installed, essentially as one of the last components to be installed. Following the installation of the roof, the closures are hung on the vehicle without their exterior body panels. The exterior body panels are lightweight components that define the color of the vehicle and are decorative only. They provide no structural improvements or waterproofing features and are the last components installed on the vehicle. Because the body panels, which are the only parts to define the vehicle's color, are the last components to be installed they are able to be installed or swapped at the final point of sale based on the color choice of the buyer at the time of purchase.
Although using lightweight panels is discussed in U.S. Pat. No. 7,000,978, these panels utilize a ridge foam core for strength and form a one-piece vehicle body (Col. 3, line 18). Similar panels are also described in U.S. Pat. No. 6,010,182 which relates to chassis and body panel structural systems for a wide variety of vehicles. The latter patent discusses a node and interlocking spaceframe, body structure system that can be hand assembled in the field and is “adapted to releasably attach non-movable vehicle body panels to the chassis” (col 1, lines 54-55). These body panels lock into the spaceframe so that the panels ‘become full load bearing members within the overall structure” (Col. 3, lines 13-14). In both of these panel constructions, however, the lightweight panels are structurally integral to the vehicle. With the assembly methodology of the present invention, the panels are attached to the structure primarily to define the look of the vehicle but contribute no additional functionality other than managing air flow around the vehicle. This enables the design to be refreshed by replacement of these panels without any effect on the structural characteristics of the vehicle. Furthermore, with the replacement of these panels and the roof system, an entirely new vehicle design can be put on the same platform.
The improvement in structural strength using the methodology of the present invention also allows for the production of a lighter vehicle, which results in improved handling and fuel efficiency. The reduced assembly complexity leads to lowered manufacturing cost and easier field serviceability with a subsequent reduction in repair costs. The simplified assembly also results in an increase in manufacturing flexibility, allowing the production of different vehicles with minimal tooling/production changes, and removes the capital intensive processes of die-stamping operations, major body shop welding operations, and the painting operations from the vehicle assembly plant. In addition, this assembly method enables point of sale customization, reducing inventory and the need for sales incentives.